MFG.com is rapidly becoming the eBay of manufacturing. In the past 12 months, $2 billion worth of gears, molds and machined parts were sourced and traded on the site. To participate, sellers pay an annual fee of $6,000 on average, and buyers pay nothing. Buyers describe the part they want and submit digital renderings, and industrial suppliers bid for the business. The site is on track to make $25 million in revenue, and book its first profit, this year.